java.util.concurrent

Interface ConcurrentMap<K,V>

Type Parameters:

K - the type of keys maintained by this map

V - the type of mapped values

All Superinterfaces:

Map<K,V>

All Known Subinterfaces:

ConcurrentNavigableMap<K,V>

All Known Implementing Classes:

ConcurrentHashMap, ConcurrentSkipListMap

public interface ConcurrentMap<K,V>
extends Map<K,V>

A Map providing additional atomic putIfAbsent, remove, and replace methods.

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentMap as a key or value happen-before actions subsequent to the access or removal of that object from the ConcurrentMap in another thread.

This interface is a member of the Java Collections Framework.

Since:

1.5

Author:

Doug Lea

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry<K,V>

Method Summary

Modifier and Type	Method and Description
V	putIfAbsent(K key, V value) If the specified key is not already associated with a value, associate it with the given value.
boolean	remove(Object key, Object value) Removes the entry for a key only if currently mapped to a given value.
V	replace(K key, V value) Replaces the entry for a key only if currently mapped to some value.
boolean	replace(K key, V oldValue, V newValue) Replaces the entry for a key only if currently mapped to a given value.

Methods inherited from interface java.util.Map

clear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, entrySet, equals, forEach, get, getOrDefault, hashCode, isEmpty, keySet, merge, put, putAll, remove, replaceAll, size, values

Method Detail

putIfAbsent

V putIfAbsent(K key,
            V value)

If the specified key is not already associated with a value, associate it with the given value. This is equivalent to

 if (!map.containsKey(key))
   return map.put(key, value);
 else
   return map.get(key);

except that the action is performed atomically.

Specified by:

putIfAbsent in interface Map<K,V>

Parameters:

key - key with which the specified value is to be associated

value - value to be associated with the specified key

Returns:

the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)

Throws:

UnsupportedOperationException - if the put operation is not supported by this map

ClassCastException - if the class of the specified key or value prevents it from being stored in this map

NullPointerException - if the specified key or value is null, and this map does not permit null keys or values

IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map

remove

boolean remove(Object key,
             Object value)

Removes the entry for a key only if currently mapped to a given value. This is equivalent to

 if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
   map.remove(key);
   return true;
 } else
   return false;

except that the action is performed atomically.

Specified by:

remove in interface Map<K,V>

Parameters:

key - key with which the specified value is associated

value - value expected to be associated with the specified key

Returns:

true if the value was removed

Throws:

UnsupportedOperationException - if the remove operation is not supported by this map

ClassCastException - if the key or value is of an inappropriate type for this map (optional)

NullPointerException - if the specified key or value is null, and this map does not permit null keys or values (optional)

replace

boolean replace(K key,
              V oldValue,
              V newValue)

Replaces the entry for a key only if currently mapped to a given value. This is equivalent to

 if (map.containsKey(key) && Objects.equals(map.get(key), oldValue)) {
   map.put(key, newValue);
   return true;
 } else
   return false;

except that the action is performed atomically.

Specified by:

replace in interface Map<K,V>

Parameters:

key - key with which the specified value is associated

oldValue - value expected to be associated with the specified key

newValue - value to be associated with the specified key

Returns:

true if the value was replaced

Throws:

UnsupportedOperationException - if the put operation is not supported by this map

ClassCastException - if the class of a specified key or value prevents it from being stored in this map

NullPointerException - if a specified key or value is null, and this map does not permit null keys or values

IllegalArgumentException - if some property of a specified key or value prevents it from being stored in this map

replace

V replace(K key,
        V value)

Replaces the entry for a key only if currently mapped to some value. This is equivalent to

 if (map.containsKey(key)) {
   return map.put(key, value);
 } else
   return null;

except that the action is performed atomically.

Specified by:

replace in interface Map<K,V>

Parameters:

key - key with which the specified value is associated

value - value to be associated with the specified key

Returns:

the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)

Throws:

UnsupportedOperationException - if the put operation is not supported by this map

ClassCastException - if the class of the specified key or value prevents it from being stored in this map

NullPointerException - if the specified key or value is null, and this map does not permit null keys or values

IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map